Information recording device and information recording method

ABSTRACT

Based on a recording signal, a recording pulse signal, which includes a top pulse located at a front end portion and having a first magnitude, a last pulse located at a back end portion and having the first magnitude, and an intermediate bias portion located between the top pulse and the last pulse and having a second magnitude, is generated. Based on the recording pulse signal, a light source is controlled, and a laser pulse is irradiated on a recording medium. Recording marks corresponding to the recording signal are formed on the recording medium. In generating the recording pulse signal, when the recording medium is rotationally driven, a position of the top pulse is shifted ahead of a position of the top pulse when the recording medium is rotationally driven at the first rotation speed, when the recording medium is rotationally driven at the second control speed.

FIELD OF THE INVENTION

This invention relates to a technique for recording information on anoptical disc using a laser light or other means.

DESCRIPTION OF RELATED ART

Onto a recordable or rewritable optical disc such as a DVD-R(DVD-Recordable) or a DVD-RW (DVD-Rerecordable), information is recordedthereon by irradiating a laser light on a recording surface of the disc.At the areas on the recording surface of the optical disc where thelaser light is irradiated, the property of the optical recording mediumforming the optical disc is physically changed because of the increasedtemperature. This produces recording marks on the recording surface.

Namely, the laser light is modulated by recording pulses having timewidths corresponding to information to be recorded, so that the laserpulses having lengths corresponding to information to be recorded aregenerated and irradiated on the optical disc. Thus, recording markshaving lengths corresponding to the information to be recorded can beformed on the optical disc.

One approach recently used is control of a laser power to form arecording mark by a pulse train portion having a plurality of shortpulses (referred to as “pulse train”), rather than by a single laserpulse. This approach, called “write strategy”, introduces less heataccumulation on the recording surface of the optical disc in comparisonwith the approach irradiating a single recording laser pulse. Therefore,uniform temperature distribution can be achieved on the recordingsurface on which the recording marks are formed. This can preventundesired teardrop-shaped recording marks from being formed, and enablesthe formation of the recording marks of preferred shape.

The above-mentioned recording pulse train includes a plurality of pulseswhose magnitudes vary between a certain read (read out) power level anda write (write in or recording) power level. That is, based on arecording signal, the areas on the recording surface of the optical discwhere no recording marks are to be formed (referred to as “spaceportions” hereafter) are irradiated with the laser light of the readpower. The areas on the recording surface of the optical disc whererecording marks are to be formed (referred to as “mark portions”hereafter) are irradiated with the laser light of the powercorresponding to the recording pulse train whose magnitudes vary betweenthe read power and the write power. Consequently, the recording marksare formed on the recording surface.

FIG. 15 shows an example of the recording pulse waveform by theabove-mentioned write strategy. The example in FIG. 15 is the recordingpulse waveform of the portion for recording a mark 7 T in the recordingdata. As shown in FIG. 15, the recording pulse is formed by a single toppulse 90 and a subsequent pulse train (referred to as “multi pulse”) 92including a plurality of pulses 91. For example, the top pulse 90 has1.5 T pulse width, and each pulse 91 of the subsequent pulse train 92has 0.5 T pulse width. Both the top pulse 90 and the pulse train 92 arepluses whose magnitudes vary between a write power Pw and a read powerPr.

The top pulse 90 serves as to perform preheat and to form a markstarting portion on the recording surface of the optical disc for thepurpose of recording the marks. By irradiating a recording lasercorresponding to the top pulse 90 of 1.5 T pulse width, the top pulse 90brings the recording surface of the optical disc to a melting point.Afterward, the subsequent pulse train 92 forms marks havingpredetermined length on the recording surface. For example, the pulsetrain 92 is formed by a series of the plurality of pulses 91 having 0.5T pulse width (one period including ON and OFF periods is 1 T). Thereby,on the recording surface of the optical disc, 0.5 T laser irradiation,0.5 T cooling, 0.5 T laser irradiation and . . . are repeated, and thelength of the formed mark is controlled.

In the method of using the recording pulse waveform shown in FIG. 15, byassuming the mark length to be recorded as “n”, the recording pulse isformed by the single top pulse 90 and the pulse train 92 including the(n-3) pulses 91. By generating the above-mentioned recording pulse inaccordance with the mark length to be recorded to drive the recordinglaser, the marks having the predetermined length are recorded on therecording surface of the optical disc.

Recently, as for a computer peripheral equipment such as a DVD-R drive,a high transmission rate is desired. For obtaining the high transmissionrate, it is necessary that disc rotation speed (liner speed) is higher.Accordingly, it is also necessary that the laser power at the time ofrecording is increased.

However, in various methods, such as the example in FIG. 15, the widthof the recording mark is generally expanded according to the increasethe recording laser power. Increasing the recording mark width causesproblems as follows.

On the DVD-R disc, the recording track (groove) is wobbled at a constantfrequency, and address pits called “land prepits” (referred to as “LPPs”hereafter) are formed on a land track between the recording tracks. Bythe wobbling and the LPP, control of the disc rotation, generating of arecording clock and obtaining information necessary for recording thedata, such as a recording address, become possible during recording.However, due to the increase of the recording mark width, the recordingmarks reach a recording film on the lands and the LPPs, which sometimescauses distortion and destruction of the LPPs. As a result, a recordingand reproducing apparatus cannot detect the LPPs, and recording andreproduction on the disc becomes impossible.

Also, on a disc called “DVD+R”, due to increase of the recording markwidth, leaking of a wobble signal occurs to the recording signal.Thereby, signal quality becomes worse, and the address signal modulatedinto the wobble signal is not read out.

SUMMARY OF THE INVENTION

The present invention has been achieved in order to solve the aboveproblems. It is an object of this invention to provide an informationrecording apparatus and an information recording method capable ofrecording marks of appropriate shape at the time of high-speedrecording.

According to one aspect of the present invention, there is provided aninformation recording apparatus which irradiates a laser light on arecording medium and forms recording marks according to a recordingsignal, including: a driving source which rotationally drives therecording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, a last pulse located at a back endportion and having the first magnitude, and an intermediate bias portionlocated between the top pulse and the last pulse and having a secondmagnitude, based on the recording signal; and a control unit whichirradiates a laser pulse on the recording medium by controlling thelight source based on the recording pulse signal, wherein the signalgenerating unit shifts a position of the top pulse ahead of a positionof the top pulse in a case that the recording medium is rotationallydriven at the first rotation speed, when the recording medium isrotationally driven at the second rotation speed.

According to a similar aspect of the present invention, there isprovided an information recording method which irradiates a laser lightfrom a light source on a recording medium and forms recording marksaccording to a recording signal, including: a driving process whichrotationally drives the recording medium at least at a first rotationspeed and a second rotation speed higher than the first rotation speed;a signal generating process which generates a recording pulse signalincluding a top pulse located at a front end portion and having a firstmagnitude, a last pulse located at a back end portion and having thefirst magnitude, and an intermediate bias portion located between thetop pulse and the last pulse and having a second magnitude, based on therecording signal; and a control process which irradiates a laser pulseon the recording medium by controlling the light source based on therecording pulse signal, wherein the signal generating process shifts aposition of the top pulse ahead of a position of the top pulse in a casethat the recording medium is rotationally driven at the first rotationspeed, when the recording medium is rotationally driven at the secondrotation speed.

In accordance with the above information recording apparatus and amethod thereof, information is recorded by irradiating the laser lightto the recording medium such as a DVD-R and forming the recording marks,for example. In that case, recording can be performed at least at twokinds of speed. At the time of recording the information at a firstrecording speed, the recording medium is rotationally driven at thefirst rotation speed. At the time of recording the information at asecond recording speed higher than the first recording speed, therecording medium is rotationally driven at the second rotation speed.The recording pulse signal generated based on the recording signalincludes the top pulse located at the front end portion and having afirst magnitude, the last pulse located at a back end portion and havingthe first magnitude, and the intermediate bias pulse portion locatedbetween the top pulse and the last pulse and having a second magnitude.The light source is controlled based on the generated recording pulsesignal, and the laser pulse is irradiated on the recording medium.Thereby, the recording marks corresponding to the recording signal areformed on the recording medium.

In the generating process of the recording pulse signal, when therecording medium is rotationally driven at the second rotation speed,the position of the top pulse is shifted ahead of the position of thetop pulse when the recording medium is rotationally driven at the firstrotation speed. At the time of the high-speed recording in which therecording medium is driven at the second rotation speed higher than thefirst rotation speed, by shifting the position of the top pulse ahead,it can be prevented that the recording marks formed on the recordingmedium are shortened. As a result, recording marks of appropriate shapecan be formed at the time of the high-speed recording, too.

In the above information recording apparatus and the method, it ispreferred that the shift quantity of the top pulse is a value between0.1 T and 2.0 T.

In one mode of the above information recording apparatus and the method,it is preferred that the signal generating unit sets the first magnitudeto a value between 1.1 times and 2.0 times of the second magnitude.

According to another aspect of the present invention, there is providedan information recording apparatus which irradiates a laser light on arecording medium and forms recording marks according to a recordingsignal, including: a driving source which rotationally drives therecording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, a last pulse located at a back endportion and having the first magnitude, and an intermediate bias portionlocated between the top pulse and the last pulse and having a secondmagnitude, based on the recording signal; and a control unit whichirradiates a laser pulse on the recording medium by controlling thelight source based on the recording pulse signal, wherein the signalgenerating unit shift a position of the last pulse behind a position ofthe last pulse in a case that the recording medium is rotationallydriven at the first rotation speed, when the recording medium isrotationally driven at the second rotation speed.

According to a similar aspect of the present invention, there isprovided an information recording method which irradiates a laser lightfrom a light source on a recording medium and forms recording marksaccording to a recording signal, including: a driving process whichrotationally drives the recording medium at least at a first rotationspeed and a second rotation speed higher than the first rotation speed;a signal generating process which generates a recording pulse signalincluding a top pulse located at a front end portion and having a firstmagnitude, a last pulse located at a back end portion and having thefirst magnitude, and an intermediate bias portion located between thetop pulse and the last pulse and having a second magnitude, based on therecording signal; and a control process which irradiates a laser pulseon the recording medium by controlling the light source based on therecording pulse signal, wherein the signal generating process shifts aposition of the last pulse behind a position of the last pulse in a casethat the recording medium is rotationally driven at the first rotationspeed, when the recording medium is rotationally driven at the secondrotation speed.

In accordance with the above information recording apparatus and themethod thereof, the information is recorded by irradiating the laserlight to the recording medium such as the DVD-R and forming therecording marks, for example. In that case, recording can be performedat least at two kinds of speed. At the time of recording the informationat a first recording speed, the recording medium is rotationally drivenat the first rotation speed. At the time of recording the information ata second recording speed higher than the first recording speed, therecording medium is rotationally driven at the second rotation speed.The recording pulse signal generated based on the recording signalincludes the top pulse located at a front end portion and having a firstmagnitude, the last pulse located at a back end portion and having thefirst magnitude, and an intermediate bias portion located between thetop pulse and the last pulse and having a second magnitude. The lightsource is controlled based on the generated recording pulse signal, andthe laser pulse is irradiated on the recording medium. Thereby, therecording marks corresponding to the recording signal are formed on therecording medium.

In the generating process of the recording pulse signal, when therecording medium is rotationally driven at the second rotation speed,the position of the last pulse is shifted behind the position of thelast pulse, when the recording medium is rotationally driven at thefirst rotation speed. At the time of the high-speed recording at whichthe recording medium is driven at the second rotation speed higher thanthe first rotation speed, by shifting the position of the last pulsebehind, it can be prevented that the recording marks formed on therecording medium are shortened. As a result, recording marks ofappropriate shape can be formed at the time of the high-speed recording,too.

In the above information recording apparatus and the method thereof, itis preferred that the shift quantity of the last pulse is a valuebetween 0.1 T and 2.0 T.

In another method of the above information recording apparatus and themethod thereof, it is preferred that the signal generating unit sets thefirst magnitude to a value between 1.1 times and 2.0 times of the secondmagnitude.

According to still another aspect of the present invention, there isprovided an information recording apparatus which irradiates a laserlight on a recording medium and forms recording marks according to arecording signal, including: a driving source which rotationally drivesthe recording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, and a pulse train portion havingone or a plurality of pulse following the top pulse, based on therecording signal; and a control unit which irradiates a laser pulse onthe recording medium by controlling the light source based on therecording pulse signal, wherein the signal generating unit shifts aposition of the top pulse ahead of a position of the top pulse in a casethat the recording medium is rotationally driven at the first rotationspeed, when the recording medium is rotationally driven at the secondrotation speed.

According to a similar aspect of the present invention, there isprovided an information recording method which irradiates a laser lightfrom a light source on a recording medium and forms recording marksaccording to a recording signal, including: a driving process whichrotationally drives the recording medium at least at a first rotationspeed and a second rotation speed higher than the first rotation speed;a signal generating process which generates a recording pulse signalincluding a top pulse located at a front end portion and having a firstmagnitude and, and a pulse train portion having one or a plurality ofpulse following the top pulse, based on the recording signal; and acontrol process which irradiates a laser pulse on the recording mediumby controlling the light source based on the recording pulse signal,wherein the signal generating process shifts a position of the top pulseahead of a position of the top pulse in a case that the recording mediumis rotationally driven at the first rotation speed, when the recordingmedium is rotationally driven at the second rotation speed.

In accordance with the above information recording apparatus and amethod thereof, the information is recorded by irradiating the laserlight to the recording medium such as the DVD-R and forming therecording marks, for example. In that case, recording can be performedat least at two kinds of speed. At the time of recording the informationat a first recording speed, the recording medium is rotationally drivenat the first rotation speed. At the time of recording the information ata second recording speed higher than the first recording speed, therecording medium is rotationally driven at the second rotation speed.The recording pulse signal generated based on the recording signalincludes the top pulse located at the front end portion and having thefirst magnitude, and the pulse train portion having one or the pluralityof pulse following the top pulse. The light source is controlled basedon the generated recording pulse signal, and the laser pulse isirradiated on the recording medium. Thereby, the recording markscorresponding to the recording signal are formed on the recordingmedium.

In the generating process of the recording pulse signal, when therecording medium is rotationally driven at the second rotation speed,the position of the top pulse is shifted ahead of the position of thetop pulse in the case that the recording medium is rotationally drivenat the first rotation speed. At the time of the high-speed recording inwhich the recording medium is driven at the second rotation speed higherthan the first rotation speed, by shifting the position of the top pulseahead, it can be prevented that the recording marks formed on therecording medium is shortened. As a result, recording marks ofappropriate shape can be formed at the time of the high-speed recording.

In the above information recording apparatus and the method thereof, itis preferred that the shift quantity of the last pulse is a valuebetween 0.1 T and 1.5 T.

In another method of the above information recording apparatus and themethod thereof, it is preferred that the signal generating unit sets aduty ratio of the pulse train portion to a value between 0.3 and 0.9.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a configuration of aninformation recording and reproducing apparatus to which the presentinvention is applied.

FIG. 2 is a block diagram showing a configuration of a recording controlunit shown in FIG. 1.

FIG. 3 is a diagram showing a configuration of an LD driver shown inFIG. 2.

FIG. 4 is a graph showing a relation between a driving current given toa laser diode and an output power.

FIG. 5 is a waveform diagram showing an example of a recording pulsewaveform by a basic write strategy.

FIG. 6 is a waveform diagram showing recording pulse waveforms of 3 T to11 T and 14 T lengths by a basic write strategy.

FIGS. 7A to 7E are waveform diagrams showing examples of recording pulsewaveforms by an improved write strategy of the present invention.

FIG. 8 is a waveform diagram showing recording pulse waveforms of 3 T to11 T and 14 T lengths by the improved write strategy of the presentinvention.

FIGS. 9A to 9D show characteristics by the improved write strategy ofthe present invention in comparison with characteristics of comparativeexamples.

FIG. 10 is a diagram for explaining AR.

FIGS. 11A to 11C show reproducing signal waveforms by the improved writestrategy of the present invention in comparison with reproducing signalwaveforms of comparative examples.

FIGS. 12A to 12D show examples that the improved write strategy of thepresent invention is applied to a normal write strategy.

FIGS. 13A to 13D show exampled that the improved write strategy of thepresent invention is applied to a normal write strategy.

FIGS. 14A to 14E are waveform diagrams showing another examples ofrecording pulse waveforms by the improved write strategy of the presentinvention.

FIG. 15 shows a waveform example of a recording pulse waveform by anormal write strategy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedbelow with reference to the attached drawings.

[Configuration of Apparatus]

FIG. 1 schematically shows a whole configuration of the informationrecording and reproducing apparatus according to the embodiment of thepresent invention. An information recording and reproducing apparatus 1records the information on an optical disc D, and reproduces theinformation from the optical disc D. For example, the optical disc D maybe a CD-R (Compact Disc-Recordable) and a DVD-R for recording only once,and a CD-RW (Compact Disc-Rewritable) and a DVD-RW that allow forrepeated erasing and recording of information.

The information recording and reproducing apparatus 1 includes anoptical pickup 2 which irradiates a recording beam and a reproducingbeam on the optical disc D, a spindle motor 3 which controls rotation ofthe optical disc D, a recording control unit 10 which controls therecording of the information on the optical disc D, a reproducingcontrol unit 20 which controls reproduction of the information alreadyrecorded on the optical disc D, and a servo control unit 30 whichexecutes various kinds of servo control including a spindle servo whichcontrols rotation of the spindle motor 3, and a focus servo and atracking servo, both of which are relative position control of theoptical pickup 2 with respect to the optical disc D.

The recording control unit 10 receives the recording signal andgenerates a driving signal SD for driving a laser diode inside theoptical pickup 2 by a process described below, and supplies the signalSD to the optical pickup 2.

The reproducing control unit 20 receives a read-out RF signal Srf whichis outputted from the optical pickup 2, and generates and outputs areproducing signal by executing a predetermined demodulating process anda decoding process to the signal Srf.

The servo control unit 30 receives the read-out RF signal Srf from theoptical pickup 2, and, based on the signal, supplies a servo signal S1such as a tracking error signal and a focus signal to the optical pickup2, and also supplies a spindle servo signal S2 to the spindle motor 3.Thus, various kinds of servo processes, such as a tracking servo, afocus servo and a spindle servo, are executed.

In the present invention, which mainly relates to the recording methodby the recording control unit 10, various kinds of known methods can beapplied to the reproducing control and the servo control. Therefore,explanations thereof are not given in detail here.

Though FIG. 1 illustrates the information recording and reproducingapparatus as the embodiment of the present invention, it is alsopossible to apply the present invention to an information recordingapparatus dedicated to recording.

FIG. 2 shows internal configurations of the optical pickup 2 and therecording control unit 10. As shown in FIG. 2, the optical pickup 2includes a laser diode LD which generates the recording beam forrecording the information on the optical disc D and the reproducing beamfor reproducing the information from the optical disc D, and a frontmonitor diode (FMD) 16 which receives the laser light emitted from thelaser diode LD and outputs a laser power level signal LDoutcorresponding to the laser light.

The optical pickup 2 additionally includes a light detector whichreceives a reflected beam of the reproducing beam by the optical disc Dto generate the read-out RF signal Srf, and well-known components suchas an optical system which guides the recording beam, the reproducingbeam and the reflected beam to appropriate directions. However, drawingsand detailed explanations thereof are omitted here.

On the other hand, the recording control unit 10 includes a laser diode(LD) driver 12, an APC (Automatic Power Control) circuit 13, a samplehold (S/H) circuit 14 and a controller 15.

The LD driver 12 supplies, to the laser diode LD, the currentcorresponding to the recording signal, and records the information onthe optical disc D. The front monitor diode 16, which is provided nearthe laser diode LD in the optical pickup 2, receives the laser lightemitted from the laser diode LD and outputs the laser power level signalLDout indicating a level thereof.

A sample hold circuit 14 samples and holds the level of the laser powerlevel signal LDout at timing prescribed by a sample hold signal APC-S/H.Based on the output signal of the sample hold circuit 14, the APCcircuit 13 executes power control of the LD driver 12 so that the readpower level of the laser light emitted from the laser diode LD isconstant.

The controller 15 mainly performs a recording operation and an APCoperation. First, the recording operation will be explained. In therecording operation, the controller 15 generates switching signals SWR,SWW1 and SWW2 of the switches which control a current quantity suppliedto the laser diode LD, and supplies them to the LD driver 12.

FIG. 3 shows a detailed configuration of the LD driver 12. As shown inFIG. 3, the LD driver 12 includes a current source 17R for a read level,current sources 17W1 and 17W2 for a write level, and switches 18R, 18W1and 18W2.

The current source 17R for the read level flows a driving current IR formaking the laser diode LD emit the laser light with the read power, andthe driving current IR is supplied to the laser diode LD via the switch18R. Therefore, when the switch 18R is set to an ON state, the drivingcurrent IR of the read power is supplied to the laser diode LD. When theswitch 18R is set to an OFF state, supplying of the driving current IRis stopped. The quantity of the driving current IR from the currentsource 17R varies by a control signal SAPC.

The current sources 17W1 and 17W2 for the write level flow drivingcurrent IW1 and IW2, to the laser diode LD, for emitting the laser lightwith the write power respectively. The driving current IW1 is suppliedto the laser diode LD via the switch 18W1, and the driving current IW2is supplied to the laser diode LD via the switch 18W2.

In the write strategy according to the present invention, two levels ofwrite powers, i.e., a first write power Ph and a second write power Pmlower than the first write power Ph are used (see FIG. 5). When theswitch 18W1 is set to the ON state with the switch 18R in the ON state,a total driving current of the driving currents IR and IW1 is suppliedto the laser diode LD. Thereby, the laser diode is driven by the secondwrite power Pm. In addition, when the switch 18W2 is set to the ON statewith the switches 18R and 18W1 in the ON state, the driving current IW2is additionally supplied to the laser diode LD. As a result, a totaldriving current of the driving currents IR, IW1 and IW2 is flown to thelaser diode LD, and the laser diode LD is driven by the first writepower Ph. When the switch 18W1 is set to the OFF state, the supply ofthe driving current IW1 is stopped. When the switch 18W2 is set to theOFF state, the supply of the driving current IW2 is stopped.

FIG. 4 shows a relation between the driving current supplied to thelaser diode LD and the output power of the laser light emitted from thelaser diode LD. As understood from FIG. 4, when the driving current IRis supplied to the laser diode LD, the laser light is emitted with theread power PR. In that state, by further adding the driving current IW1,the laser light is emitted with the second write power Pm. By furtheradding the driving current IW2, the laser light is emitted with thefirst write power Ph.

At the time of recording the information on the optical disc, basically,the driving current IR is always supplied, and the laser light isemitted with the read power PR. Additionally, if the driving currentsIW1 and IW2 are added in accordance with the recording pulse, the firstwrite power Ph or the second write power Pm is applied, and theinformation is recorded on the optical disc.

Next, the APC operation will be explained. The APC operation is foradjusting the driving current level supplied from the LD driver 12 tothe laser diode LD so that the level of the read power of the laserlight outputted by the laser diode LD becomes constant. In detail, in along space period (e.g., 5 T to 11 T and 14 T space periods) of thespace portion of the recording signal (which is 8-16 modulated, andwhich has the mark period and the space period of 3 T to 11 T and 14 Tlengths), the driving signal SD from the recording control unit 10 isadjusted so that the level of the read power is constant.

Concretely, the APC operation is performed as follows. The controller 15generates the recording pulse corresponding to the recording signal asdescribed above, and drives the LD driver 12 by the recording pulse toemit the laser light from the laser diode LD.

The front monitor diode 16, which is provided near the laser diode LD inthe optical pickup 2, receives the laser light emitted from the laserdiode LD, and generates the laser power level signal LDout indicatingits level to supply it to the sample hold circuit 14.

The sample hold circuit 14 samples the laser power level signal LDoutsupplied from the front monitor diode 16 at the timing given by thesample hold signal APC-S/H inputted from the controller 15, and holdsits level for a predetermined period. The sample hold signal APC-S/Houtputted from the controller 15 is a pulse indicating a period(referred to as “APC period”) in which the APC is executed.

Thus, the sample hold circuit 14 holds the level of the laser powerlevel signal LDout in the APC period in the space period of therecording signal, and supplies it to the APC circuit 13. The APC circuit13 supplies the control signal SAPC to the LD driver 12 so that thelevel of the laser power level signal LDout in the APC period becomesconstant.

As shown in FIG. 3, the control signal SAPC is inputted to the currentsource 17R for the read level in the LD driver 12. Thereby, inaccordance with the control signal SAPC, the current IR flowing from thecurrent source 17R for the read level varies. Namely, the APC isexecuted so that the read power level obtained by the laser diode LDbecomes constant.

[Write Strategy]

Next, the write strategy according to the present invention will beexplained.

(Basic Write Strategy)

First, FIG. 5 shows the recording pulse waveform by a basic writestrategy. As shown in FIG. 5, the recording pulse waveform by the basicwrite strategy is formed by three portions, i.e., a top pulse 40, anintermediate bias portion 41 and a last pulse 42. In portions other thanthose portions, the recording pulse waveform is maintained at the levelof the read power PR.

The write powers of two values are utilized for the basic writestrategy. The top pulse 40 and the last pulse 42 have the first writepower Ph, and the intermediate bias portion 41 has the second writepower Pm. Though the second write power Pm is higher than the read powerPR, it is set to be lower than the first write power Ph.

The top pulse 40 preheats the recording surface of the optical disc, andforms the mark starting portion for the purpose of recording the mark. Atime width of the intermediate bias portion 41 varies in accordance withthe length of the recording data. The last pulse 42 mainly has afunction to adjust a shape of the back end portion of the mark.Basically, the length of the formed recording mark is controlled by atop pulse width Ttop, a last pulse width T1p, a width Tp from the frontend portion of the top pulse to the back end portion of the last pulse,and the first write power Ph, and the width of the formed recording markis controlled by the second write power Pm.

FIG. 6 shows the recording pulse waveform corresponding to each marklength to be recorded. The recording data is 8-16 modulated, and has themark period and the space period of 3 T to 11 T and 14 T lengths. Asshown in FIG. 6, a front edge of the recording pulse waveform is alwayslocated at the position behind 1.5 T from the front edge of therecording data, irrespective of the mark length. The recording pulsewaveforms of the recording data of 3 T and 4 T do not have theintermediate bias portion 41, and the top pulse 40 and the last pulse 42are synthesized to form the single pulse. The power of this pulse is thefirst write power Ph, which is identical to the powers of the top pulseand the last pulse.

When the recording data is equal to or larger than 5 T, the length ofthe intermediate bias portion 41 increases in accordance with eachlength. The pulse widths of the top pulse 40 and the last pulse 42 arebasically almost constant respectively, and the widths do not have to belargely varied in accordance with the recording data length, differentlyfrom the intermediate bias portion 41.

In the example of FIG. 6, when the recording data is 4 T, the top pulseand the last pulse are synthesized to form the single pulse waveform.However, as shown by a broken line 100 in FIG. 6, when the recordingdata is 4 T, the recording pulse waveform can also be determined so thatthe intermediate bias portion is provided.

When the recording speed is higher, the clock also becomes highercorrespondingly. Therefore, not only the recording data of 3 T and 4 T,but also the recording data equal to or larger than 5 T may have thesingle-pulse-type recording pulse wave forms without the intermediatebias portion.

(Improved Write Strategy)

Next, an improved write strategy of the present invention will beexplained. The improved write strategy is based on the above-mentionedbasic write strategy, and is further suitable for the high-speedrecording. For example, in an information recording apparatus capable ofrecording the information at different speeds of two or more kinds, therecording is performed at the normal speed by using the above-mentionedbasic write strategy, and the recording can be performed at a speedhigher than the normal speed by using the improved write strategy, whichwill be explained as follows.

When the disc rotation speed is increased for performing the high-speedrecording, the recording laser power also has to be increasedcorrespondingly to the increase of the disc rotation speed in order toappropriately form the recording marks. However, if the recording laserpower is increased too much, the width of the recording mark formed onthe recording track of the disc becomes wider than needed. As a result,a problem occurs, e.g., a malfunction occurs to the detection of theLPP. The improved write strategy of the present invention can form therecording marks of appropriate width, even when the disc rotation speedis increased for the high-speed recording.

As described above, it is the write power Pm of the intermediate biasportion 41 that affects the width of the formed recording mark most inthe basic write strategy. Therefore, if the write power Pm is decreased,the width of the recording mark becomes small, and a modulation can bedecreased. The modulation is a value indicating a ratio (I14/I14H) of anmagnitude I14 of the reproducing signal corresponding to a longestrecording mark and a longest space, with respect to a difference I14Hbetween a peak value and the zero level of the reproducing signalcorresponding to a longest space portion (14T space). According to aDVD-R standard book, the modulation equal to or larger than 0.60 (60%)is required.

However, if the modulation is decreased by decreasing only the writepower Pm of the intermediate bias portion 41, a distortion occurs to thereproduced waveform. As a result, problems occur, such as the increaseof jitters in recording and reproduction, the increase of read-outerrors of the recording marks, the increase of error rates, and thelike. Additionally, if the reproducing process is executed by using adistorted reproduced waveform, a probability of erroneous detection ofthe recording data is increased. Further, if the recording is performedby decreasing only the write power Pm in the intermediate bias portion41, the shape of the recording mark formed on the disc becomes wide atthe front end portion and the back end portion corresponding to the toppulse 40 and the last pulse 42, and becomes narrow only at theintermediate portion corresponding to the intermediate bias portion 41.The wide front and back end portions give an adverse effect to the shapeof the LPP.

In order to overcome such problem, if not only the level of the writepower Pm in the intermediate bias portion 41 but also the level of thewrite power Ph corresponding to the top pulse 40 and the last pulse 42are decreased, the distortion of the reproduced wave form can besuppressed. However, as described above, the write power Phcorresponding to the top pulse 40 and the last pulse 42 affects thelength of the formed recording mark. Therefore, if the write power Phcorresponding to the top pulse 40 and the last pulse 42 is decreased forsuppressing the distortion of the reproduced waveform, the length of therecording mark becomes short, and the erroneous detection of therecording data may occur.

Therefore, in the improved write strategy of the present invention, thewidth Tp from the front end portion of the top pulse to the back endportion of the last pulse is enlarged by shifting the position of thetop pulse 40 ahead by a predetermined quantity or by shifting theposition of the last pulse 42 behind by a predetermined quantity, and itis thereby prevented that the length of the recording mark is shortened.Namely, in the improved write strategy of the present invention, twoimproved points below are prescribed to be simultaneously performed:

(Improved point 1): Shifting the position of the top pulse 40 ahead by apredetermined quantity, or shifting the position of the last pulse 42behind by a predetermined quantity; and

(Improved point 2): Decreasing the write power Pm corresponding to theintermediate bias portion 41.

In addition to the above two points, as the need arises, an improvedpoint 3 below is performed:

(Improved point 3): Decreasing the write power Ph corresponding to thetop pulse 40 and the last pulse 42.

According to the improved write strategy, extension of the recordingmark width is suppressed by reducing the write power Pm of theintermediate bias portion 41. Though the distortion occurs to thereproduced waveform by reducing the write power Pm, the distortion issuppressed by reducing the write power Ph corresponding to the top pulse40 and the last pulse 42 as the need arises. Though the lengths of thewhole recording marks are shortened by reducing the write power Ph, byshifting the position of the top pulse 40 ahead or shifting the positionof the last pulse 42 behind according to the shortened quantity, thelengths of the whole formed recording marks are maintained toappropriate lengths. As described above, at the time of the high-speedrecording, even when the recording laser power is increased, theextension of the recording mark width can be prevented, and theoccurrence of the distortion can also be suppressed.

FIGS. 7A to 7E show examples of the recording pulse waveforms by theimproved write strategy of the present invention. FIG. 7A is thewaveform of the recording data, and FIG. 7B is the recording pulsewaveform by the basic write strategy. FIGS. 7C and 7D are the examplesof the recording pulse waveforms by the improved write strategy, andFIG. 7E is a clock waveform.

As for the recording pulse waveform by the improved write strategy shownin FIG. 7C, the position of the top pulse 40 is shifted ahead by 0.5 Tin comparison with the position of the top pulse 40 of the recordingpulse waveform by the basic write strategy shown in FIG. 7B. It is notedthat the shift quantity is merely an example, and the value between 0.1T to 1.5 T can be taken dependently upon the optical disc. The writepower Pm of the intermediate bias portion 41 by the improved writestrategy becomes smaller than the write power Pm of the intermediatebias portion 41 of the recording pulse waveform by the basic writestrategy. Moreover, the write power Ph of the top pulse 40 and the lastpulse 42 by the improved write strategy becomes smaller than the writepower Ph of the top pulse 40 and the last pulse 42 of the recordingpulse waveform by the basic write strategy, and can take the value of1.1 to 2.0-times of the write power Pm of the intermediate bias portion41 by the improved write strategy.

On the other hand, in the example of the recording pulse waveform by theimproved write strategy shown in FIG. 7D, the position of the last pulse42 is shifted behind by 0.5 T in comparison with the example of therecording pulse waveform by the basic write strategy shown in FIG. 7B.The shift quantity is merely an example, and can take the value between0.1 T and 1.5 T dependently upon the optical disc. The write power Pm ofthe intermediate bias portion 41 becomes smaller than the write power Pmof the intermediate bias portion 41 of the recording pulse waveform bythe basic write strategy. Further, the write power Ph of the top pulse40 and the last pulse 42 of the recording pulse waveform becomes smallerthan the write power Ph of the top pulse 40 and the last pulse 42 of therecording pulse waveform by the basic write strategy, and can take thevalue between 1.1 times and 2.0 times of the write power Pm of theintermediate bias portion 41 by the improved write strategy. Those areidentical to the example of the recording pulse waveform shown in FIG.7C.

In the improved write strategy of the present invention, it isdispensable to reduce the write power Ph corresponding to the top pulse40 and the last pulse 42 (i.e., the Improved point 3). Basically, whenthe quantity of reducing the write power Pm of the intermediate biasportion 41 is large, unless the write power Ph is reduced to some extentin accordance with the quantity, the distortion of the signal waveformbecomes large. In the present invention, whether the write power Ph isreduced or not, or how much the write power Ph is reduced if reduced aredetermined dependently on the quantity of shifting the top pulse or thelast pulse by the Improved point 1, and on the quantity of reducing thewrite power Pm of the intermediate bias portion by the Improved point 2.

FIG. 8 shows the recording pulse waveforms corresponding to therecording data 3 T to 11 T and 14 T by the improved write strategy ofthe present invention. It is noted that the recording pulse waveforms of3 T to 11 T and 14 T by the basic write strategy at the same recordingspeed are indicated by broken lines, for the sake of comparison.According to the present improved write strategy, the recording pulsewaveforms corresponding to the recording data of 3 T and 4 T do notinclude the intermediate bias portions, but the recording pulsewaveforms may include the intermediate bias portions. As the speedincreases (e.g., 6-times speed, 8-times speed, . . . ) at the time ofthe high-speed recording, even the recording pulse waveformcorresponding to much longer recording data (e.g., 5 T, 6 T, . . . ) mayinclude no intermediate bias portion.

In the examples shown in FIGS. 7A to 7E, as for the recording pulsewaveform corresponding to the recording mark of 7 T, the top pulse isshifted ahead by 0.5 T. The shift quantity is merely the example, andthe values between 0.1 T and 1.5 T can be taken dependently upon theoptical disc, as described above. However, even when the position of thetop pulse 40 is shifted ahead, the front edge of the top pulse is neverlocated ahead of the front edge of the recording data. In the recordingpulse waveforms of 3 T to 11 T and 14 T shown in FIG. 8, the shiftquantity of the top pulse is identical. However, the top pulse may beshifted at an identical rate in accordance with the length of eachrecording pulse.

Next, characteristics obtained by the improved write strategy will beexamined in comparison with characteristics obtained by comparativeexamples in which the basic write strategy is used, with reference toFIGS. 9A to 9D. In the characteristic graphs shown in FIGS. 9A to 9D,STG1 indicates a characteristic in a case that the recording pulsewaveform by the basic write strategy shown in FIG. 7B is used. STG2 is acharacteristic of a comparative example in that the write power Pm ofthe intermediate bias portion 41 is made smaller and the pulse widths ofthe top pulse 40 and the last pulse 42 are made longer, in the recordingpulse waveform by the identical basic write strategy. STG3 is acharacteristic of a comparative example in that the write power Pm ofthe intermediate bias portion 41 is made much smaller than the case ofSTG2 and the pulse widths of the top pulse 40 and the last pulse 42 aremade much longer than the case of STG2, in the recording pulse waveformby the identical basic write strategy.

On the other hand, STG4 is a characteristic of the recording pulsewaveform by the improved write strategy shown in FIG. 7C, in that theposition of the top pulse 40 is shifted ahead by 0.5 T and the writepower Pm of the intermediate bias portion 41 is decreased. STG5 is alsoa characteristic of the recording pulse waveform by the improved writestrategy, in that the position of the top pulse 40 is shifted ahead by1.0 T and the write power Pm of the intermediate bias portion 41 is mademuch smaller than the case of STG4.

In FIGS. 9A and 9B, the horizontal axes indicate the write power Pm ofthe intermediate bias portion, and the vertical axes indicate themodulation. In FIGS. 9C and 9D, the horizontal axes similarly indicatethe write power Pm of the intermediate bias portion, and the verticalaxes indicate an AR. As shown in FIG. 10, the AR (Aperture Ratio afterrecording) is a ratio (AP(max)/AP(min)) of a maximum AP (max) and aminimum AP (min) of an LPP signal appearing in a push-pull signal afterrecording, and is a value indicating quality of the LPP. As the AR valuebecomes larger, an influence which the formed recording mark gives theLPP on a neighboring land becomes smaller. According to a DVD-R discstandard book, AR>15% is required. According toa DVD-RW disc standardbook, AR>10% is required.

As understood by comparing FIGS. 9A and 9B, in the characteristics STG4and STG5 by the improved write strategy, as the write power Pm of theintermediate bias portion is decreased, the modulation is decreasedcorrespondingly. On the other hand, in the characteristics STG2 and STG3of the comparative examples, the decreasing degree of the modulation inresponse to the decrease of the write power Pm of the intermediate biasportion is small, in comparison with the case of the improved writestrategy. Namely, the improved write strategy can effectively decreasethe modulation by the decrease of the write power Pm of the intermediatebias portion.

Next, as understood by comparing FIGS. 9C and 9D, in the characteristicsSTG4 and STG5 by the improved write strategy, when the write power Pm ofthe intermediate bias portion is decreased, the AR value remarkablyincreases. On the other hand, in the characteristics STG2 and STG3 ofthe comparative examples, even if the write power Pm of the intermediatebias portion is decreased, the distortion increases, and the AR valuedoes not increase so much. Therefore, the decrease of the write power Pmof the intermediate bias portion in the improved write strategy moreeffectively contributes to the increase of the AR value, and it can beprevented that the formed recording mark affects the LPPs on the landtrack.

FIGS. 11A to 11C show waveform examples of the reproducing signal of theabove-mentioned comparative examples and the improved write strategy.FIG. 11A shows the reproducing signal waveform in a case that therecording is performed by the basic write strategy (STG1) forcomparison. FIG. 11B shows the example of the reproducing signalwaveform of the mark recorded by the above-mentioned comparative example(STG3). FIG. 11C shows the example of the reproducing signal waveform ofthe mark recorded by the improved write strategy (STG5) of the presentinvention. If the waveform around a reference numeral 110 in each graphis taken notice of, though the lowest level of each waveformcorresponding to 3 T to 11 T and 14 T is equal in the reproducing signalwaveform shown in FIG. 11A, the modulation is large, and the effectgiven to the LPPs is also large. As for the reproducing signal waveformof the comparative example shown in FIG. 11B, though the modulationbecomes smaller in comparison with FIG. 11A, the lowest level of eachwaveform is not equal. The lowest levels of the reproducing signalwaveforms corresponding to the central portions of the recording markslonger than 7 T to 8 T become high, and the wave forms are distorted.This is because the long recording mark is formed with the narrow centerportion, like a shape of a gourd. On the other hand, in the example ofthe reproducing signal waveform of the improved write strategy shown inFIG. 11C, the modulation becomes small in comparison with FIG. 11A, andthe lowest level of the reproducing signal waveform of each recordingmark is equal.

As explained above, in the improved write strategy of the presentinvention, increasing of the formed recording mark width can besuppressed without the distortion occurring to the reproducing signalwaveform by:

(1) shifting the position of the top pulse ahead, or shifting theposition of the last pulse behind; and

(2) decreasing the write power Ph of the top pulse and the write powerPm of the intermediate bias portion in accordance with the shiftquantity.

[Other Applications]

The above-mentioned improved write strategy is based on the basic writestrategy as shown in FIG. 5. However, the concept of the improved writestrategy of the present invention can be similarly applied to the normalwrite strategy shown in FIG. 15, too.

FIGS. 12A to 12D and FIGS. 13A to 13D show application examples in acase that the concept of the improved write strategy of the presentinvention is applied to the normal write strategy. FIG. 12A shows therecording data waveform, and FIG. 12B shows the recording pulse waveformbefore the improvement of the normal write strategy, formed by the toppulse and the pulse train. FIG. 12C shows an example of the recordingpulse waveform in a case that the concept of the improved write strategyof the present invention is applied to the normal write strategy. Asunderstood by comparing FIGS. 12B and 12C, in the recording pulsewaveform to which the present invention is applied, the position of atop pulse 70 is shifted ahead by 0.5 T. The pulse width of each pulse 71forming a pulse train 72 is decreased. It is noted that the valuesbetween 0.3 and 0.9 can be taken dependently upon the disc as a dutyratio (width of pulse 71/period of pulse 71) of the pulse train 72. Thisis equivalent to decreasing of the level of the intermediate biasportion in the above-mentioned basic write strategy.

Also, in the examples shown in FIGS. 13A to 13D, FIG. 13A shows therecording data waveform, and FIG. 13B shows the recording pulse waveformbefore the improvement of the normal write strategy, formed by the toppulse and the pulse train. FIG. 13C shows the example of the recordingpulse waveform in the case that the concept of the improved writestrategy of the present invention is applied to the normal writestrategy.

In the examples shown in FIGS. 12A to 12D, only the top pulse 70 isshifted ahead, and the positions of the pulses 71 forming the pulsetrain 72 are not moved. However, in the examples shown in FIGS. 13A to13D, each pulse 71 forming the pulse train 72 is equally moved inaccordance with the shift quantity of the top pulse 70. Namely,according to a rate of increasing time width of the whole recordingpulses by movement of the top pulse 70, the position of each pulse 71 isshifted. Identically to FIG. 12C, the pulse width of each pulse 71forming the pulse train 72 is decreased. This is equivalent todecreasing the level of the intermediate bias portion in theabove-mentioned basic write strategy.

By the examples shown in FIGS. 12C and 13C, the effect identical to theimproved write strategy shown in FIG. 7C can be obtained.

It is noted that the present invention is not limited to theabove-mentioned embodiment. For example, according to FIG. 7C, theposition of the top pulse is shifted ahead by the predeterminedquantity, and according to FIG. 7D, the position of the last pulse isshifted behind by the predetermined quantity. However, by shifting thepositions of the top pulse and the last pulse ahead and behind,respectively, the recording mark length may be controlled to be adesired length.

As shown in FIG. 14B, when the position of the top pulse 40 of the basicwrite strategy is behind by 0.5 T with respect to the position of thetop pulse 40 of the basic write strategy shown in FIG. 7B, the positionof the top pulse 40 of the improved write strategy shown in FIG. 14C canbe shifted ahead between 0.1 T and 2.0 T, dependently upon the opticaldisc, in comparison with the top pulse of the basic write strategy shownin FIG. 14B. In that case, the write power Pm of the intermediate biasportion 41 by the improved write strategy becomes smaller than the writepower Pm of the intermediate bias portion 41 of the recording pulsewaveform by the basic write strategy, too. Further, the write power Phof the top pulse 40 and the last pulse 42 by the improved write strategybecomes smaller than the write power Ph of the top pulse 40 and the lastpulse 42 of the recording pulse waveform by the basic write strategy,and can take the value between 1.1 times and 2.0 times of the writepower Pm in the intermediate bias portion 41 by the improved writestrategy. On the other hand, the recording pulse waveform by theimproved write strategy shown in FIG. 14D indicates a state that theposition of the last pulse 42 is shifted behind by 0.1 T to 2.0 T, incomparison with the example of the recording pulse waveform by the basicwrite strategy shown in FIG. 14B, and hence the detailed explanationthereof is omitted here.

In addition, according to the above-mentioned embodiment, the presentinvention is applied to the recording pulse signal including the lastpulse 42. However, the present invention can also be applied to therecording pulse signal which does not include the last pulse 42.

As explained above, according to the improved write strategy of thepresent invention, in the recording pulse signal formed by the toppulse, the intermediate bias portion and the last pulse, the increase ofthe formed recording mark width can be suppressed without the distortionoccurring to the reproducing signal waveform, by shifting the positionof the top pulse ahead or by shifting the position of the last pulsebehind. Therefore, it can be prevented that the LPPs on the land trackneighboring the recording track are distorted and destroyed by therecording marks. Also, since the distortion does not occur to thereproducing signal waveform, jitter and an error of reading out of therecording mark can be prevented.

If the identical improvement is applied to the recording pulse waveformconfigured by the top pulse and the pulse train and the position of thetop pulse is shifted ahead, the identical effect can be obtained, too.

INDUSTRIAL APPLICABILITY

The information recording apparatus and the information recording methodaccording to the present invention can be utilized when information isrecorded on an optical disc by using the laser light and the like.

1. An information recording apparatus which irradiates a laser light ona recording medium and forms recording marks according to a recordingsignal, comprising: a driving source which rotationally drives therecording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, a last pulse located at a back endportion and having the first magnitude, and an intermediate bias portionlocated between the top pulse and the last pulse and having a secondmagnitude, based on the recording signal; and a control unit whichirradiates a laser pulse on the recording medium by controlling thelight source based on the recording pulse signal, wherein the secondmagnitude is smaller than the first magnitude, the intermediate biasportion is continuous in time to the top pulse, and the last pulse iscontinuous in time to the intermediate portion, wherein the signalgenerating unit shifts a position of the top pulse ahead of a positionof the top pulse in a case that the recording medium is rotationallydriven at the first rotation speed, when the recording medium isrotationally driven at the second rotation speed.
 2. The informationrecording apparatus according to claim 1, wherein a shift quantity ofthe top pulse is a value between 0.1 T and 2.0 T.
 3. The informationrecording apparatus according to claim 1, wherein the signal generatingunit sets the first magnitude to a value between 1.1 times and 2.0 timesof the second magnitude, when the recording medium is rotationallydriven at the second rotation speed.
 4. The information recordingapparatus according to claim 1, wherein the signal generating unitincreases a pulse width from a front end portion of the top pulse to aback end portion of the last pulse by shifting the position of the toppulse.
 5. An information recording apparatus which irradiates a laserlight on a recording medium and forms recording marks according to arecording signal, comprising: a driving source which rotationally drivesthe recording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, a last pulse located at a back endportion and having the first magnitude, and an intermediate bias portionlocated between the top pulse and the last pulse and having a secondmagnitude, based on the recording signal; and a control unit whichirradiates a laser pulse on the recording medium by controlling thelight source based on the recording pulse signal, wherein the secondmagnitude is smaller than the first magnitude, the intermediate biasportion is continuous in time to the top pulse, and the last pulse iscontinuous in time to the intermediate portion, wherein the signalgenerating unit shifts a position of the last pulse behind a position ofthe last pulse in a case that the recording medium is rotationallydriven at the first rotation speed, when the recording medium isrotationally driven at the second rotation speed.
 6. The informationrecording apparatus according to claim 5, wherein a shift quantity ofthe last pulse is a value between 0.1 T and 2.0 T.
 7. The informationrecording apparatus according to claim 5, wherein the signal generatingunit sets the first magnitude to a value between 1.1 times and 2.0 timesof the second magnitude, when the recording medium is rotationallydriven at the second rotation speed.
 8. The information recordingapparatus according to claim 5, wherein the signal generating unitincreases a pulse width from a front end portion of the top pulse to aback end portion of the last pulse by shifting the position of the toppulse.
 9. An information recording apparatus which irradiates a laserlight on a recording medium and forms recording marks according to arecording signal, comprising: a driving source which rotationally drivesthe recording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a light sourcewhich emits the laser light; a signal generating unit which generates arecording pulse signal including a top pulse located at a front endportion and having a first magnitude, and a pulse train portion havingone or a plurality of pulse following the top pulse, based on therecording signal; and a control unit which irradiates a laser pulse onthe recording medium by controlling the light source based on therecording pulse signal, wherein the signal generating unit shifts aposition of the top pulse ahead of a position of the top pulse in a casethat the recording medium is rotationally driven at the first rotationspeed, when the recording medium is rotationally driven at the secondrotation speed.
 10. The information recording apparatus according toclaim 9, wherein a shift quantity of the top pulse is a value between0.1 T and 1.5 T.
 11. The information recording apparatus according toclaim 9, wherein the signal generating unit sets a duty ratio of thepulse train portion to a value between 0.3 and 0.9, when the recordingmedium is rotationally driven at the second rotation speed.
 12. Aninformation recording method which irradiates a laser light from a lightsource on a recording medium and forms recording marks according to arecording signal, comprising: a driving process which rotationallydrives the recording medium at least at a first rotation speed and asecond rotation speed higher than the first rotation speed; a signalgenerating process which generates a recording pulse signal including atop pulse located at a front end portion and having a first magnitude, alast pulse located at a back end portion and having the first magnitude,and an intermediate bias portion located between the top pulse and thelast pulse and having a second magnitude, based on the recording signal;and a control process which irradiates a laser pulse on the recordingmedium by controlling the light source based on the recording pulsesignal, wherein the second magnitude is smaller than the firstmagnitude, the intermediate bias portion is continuous in time to thetop pulse, and the last pulse is continuous in time to the intermediateportion, wherein the signal generating process shifts a position of thetop pulse ahead of a position of the top pulse in a case that therecording medium is rotationally driven at the first rotation speed,when the recording medium is rotationally driven at the second rotationspeed.
 13. The information recording method according to claim 12,wherein the signal generating process increases a to a value between 1.1times and 2.0 times of the second magnitude, when the recording mediumis rotationally driven at the second rotation speed.
 14. An informationrecording method which irradiates a laser light from a light source on arecording medium and forms recording marks according to a recordingsignal, comprising: a driving process which rotationally drives therecording medium at least at a first rotation speed and a secondrotation speed higher than the first rotation speed; a signal generatingprocess which generates a recording pulse signal including a top pulselocated at a front end portion and having a first magnitude, a lastpulse located at a back end portion and having the first magnitude, andan intermediate bias portion located between the top pulse and the lastpulse and having a second magnitude, based on the recording signal; anda control process which irradiates a laser pulse on the recording mediumby controlling the light source based on the recording pulse signal,wherein the second magnitude is smaller than the first magnitude, theintermediate bias portion is continuous in time to the top pulse, andthe last pulse is continuous in time to the intermediate portion,wherein the signal generating process shifts a position of the lastpulse behind a position of the last pulse in a case that the recordingmedium is rotationally driven at the first rotation speed, when therecording medium is rotationally driven at the second rotation speed.15. The information recording method according to claim 14, wherein thesignal generating process increases a pulse width from a front endportion of the top pulse to a back end portion of the last pulse byshifting the position of the top pulse.
 16. An information recordingmethod which irradiates a laser light from a light source on a recordingmedium and forms recording marks according to a recording signal,comprising: a driving process which rotationally drives the recordingmedium at least at a first rotation speed and a second rotation speedhigher than the first rotation speed; a signal generating process whichgenerates a recording pulse signal including a top pulse located at afront end portion and having a first magnitude and, and a pulse trainportion having one or a plurality of pulse following the top pulse,based on the recording signal; and a control process which irradiates alaser pulse on the recording medium by controlling the light sourcebased on the recording pulse signal, wherein the signal generatingprocess shifts a position of the top pulse ahead of a position of thetop pulse in a case that the recording medium is rotationally driven atthe first rotation speed, when the recording medium is rotationallydriven at the second rotation speed.